1. Field of the Invention
The present invention relates to a technical field of image processing and, more particularly, to an automatic flicker detection and correction apparatus and method in a video capture device.
2. Description of Related Art
Typically, the illuminants have different frequency flickers due to the different AC frequencies in different countries. The AC frequencies are essentially divided into two types: 60 Hz such as in Taiwan where a light has a period of 1/120 second per flicker, and 50 Hz such as in China where a light has a period of 1/100 second per flicker. For capturing an image by a CMOS video capture device under such an environment, every horizontal line of an image frame has the uniform exposure amount when the exposure time is set to a multiple of one flicker period of environment lighting, and no flicker appears on the image frame. However, flicker may occur since the exposure amount on every line of the image frame is not uniform when the exposure time is not equal to a multiple of one flicker period of environment lighting.
To overcome the flicker on the image captured by the CMOS video capture device, US Patent Application Publication No. 2007/0153094 has disclosed an “Automatic flicker correction in an image capture device”, which uses the differences of the total brightness of every horizontal line of two adjacent frames to detect fixed frequency flicker, and the detected frequency to correct the exposure time of the image capture device when the fixed frequency flicker is detected.
However, such a correction cannot detect the original frequency after the differences of the total brightness of every line, which are small or even almost zero when the flicker effect on the image caused by illumination source is very light, are passed through a low pass filter (LPF). In addition, for finding the differences of the total brightness of every line of the adjacent frames, the total brightness of every line of the first frame is temporarily stored in the memory, and if the size (640×480) of a popular VGA frame is considered, the memory size required for storing 480 brightness values (in the way of 18 bits per brightness value) is 8640 bits (=1080 bytes). After the differences of the total brightness of all lines are obtained and passed through the LPF, the differences are further passed through a derivative calculator, which requires a huge amount of computation and thus takes much time to affect the normal display rate.
Therefore, it is desirable to provide an improved detection and correction apparatus to mitigate and/or obviate the aforementioned problems.